The invention relates to a bearing arrangement having at least two fluid pressure bearings which include at least one membrane, which is formed as the supporting end and which is formed to have a concave configuration because of the bearing pressure. The invention also relates to a bearing base body which is supported on the two fluid pressure bearings. Bearing arrangements of this kind have already been known for a long time and are utilized especially for machines where a high-precision support is required such as in coordinate measuring apparatus. The high-precision support is possible with the above-mentioned fluid pressure bearings because the bearing gap in fluid pressure bearings of this kind is held substantially constant by the deformability of the membranes independently of the load of the bearing.
Fluid pressure bearings of this kind, which are used in such bearing arrangements, are known, for example, from U.S. Pat. No. 4,449,834; U.S. Pat. No. 5,199,796; U.S. Pat. No. 4,560,213; and, U.S. Pat. No. 4,045,098.
All fluid pressure bearings referred to in the above publications have in common that they have a ball at the end of the fluid pressure bearing which faces away from the membrane. A support pin having an inner conical surface is supported on the ball so that the fluid pressure bearing is rotatably movable about the pin. The support pin itself is usually provided with a thread which threadably engages the bearing base body so that the elevation of the fluid pressure bearing relative to the bearing base body can be additionally changed. In this way, it is possible to secure a plurality of different fluid pressure bearings of the above-mentioned type on one and the same bearing base body. The fluid pressure bearings can be simply adjusted in that the distance of the fluid pressure bearing from the bearing base body is changed by rotating the support pins on the one hand and the particular bearings align themselves via the rotationally movable connection to the support pin on the guide surface on the other hand.
Another characteristic of the fluid pressure bearings known from the above publications is that, in all known fluid pressure bearings, the bearing housing is so configured that the membrane, which is formed as the support end, and that end of the bearing housing, on which the bearing base body is braced via the above-mentioned ball and the support pin, are two different components.
The known fluid pressure bearings function quite well especially in coordinate measuring apparatus. However, it has been shown that the stiffness of the fluid pressure bearings to date is no longer sufficient with the ever increasing quality requirements imposed on the precision of the coordinate measuring apparatus.
Starting from the above, it is an object of the invention to provide a bearing arrangement of the known type but wherein the stiffness can be considerably increased when utilizing the above-mentioned fluid pressure bearings.
The bearing arrangement of the invention includes: at least two fluid pressure bearings; a rigidly configured base body journalled on the fluid pressure bearings; each one of the fluid pressure bearings having a membrane defining a supporting end thereof; a pressure supply for supplying fluid under pressure to the bearings to cause the membranes to concavely deform and support the bearings and the rigid base body; at least one of the fluid pressure bearings having a one-piece bearing housing which includes the membrane thereof; and, the base body and the one-piece bearing housing conjointly defining a direct connection therebetween.
A significant feature of the bearing arrangement is especially that at least one of the fluid pressure bearings has a bearing housing, which is configured as one piece and which includes at least the membrane and that this bearing housing is directly connected to the bearing base body.
In this way, a series of significant advantages results compared to the known bearing arrangements. The bearing housing, which is configured as one piece, is connected directly to the bearing base body. For this reason, a significantly greater stiffness of the entire bearing results because the above-mentioned ball as well as the support pin are no longer needed and especially these components have considerably limited the stiffness of the entire bearing arrangement. Because the support pin and the ball are not needed, the bearing must no longer be centrally journalled; instead, the bearing can also be journalled in its outer edge regions which likewise contributes significantly to the stability of the bearing. Because the bearing housing is one piece, significant manufacturing and assembly advantages result because the bearing housing can be produced in only a single manufacturing operation and an assembly for the completion of the bearing housing can be completely avoided.
In principle, all other fluid pressure bearings can be likewise so configured in that the bearing housing is connected to the bearing base body. Alternatively, the other fluid pressure bearings or parts thereof can be configured in the conventional manner which is especially then purposeful when the particular fluid pressure bearings are used as a counter support.
At this point, the term bearing base body should be clearly described. The bearing base body is a rigid body which is mounted on at least two fluid pressure bearings. The bearing base body can assume different forms. For example, the base body can be a body which does not require much space and especially functions to fix the fluid pressure bearing as is the case in the embodiments described with respect to the drawings hereinafter. The bearing base body can, however, also include the entire component to be journalled which, for example, is the case when an elongated component is intended to be journalled at both of its ends. It is understood that the rigid bearing base body need not be configured as one piece; instead, the rigid bearing base body can be assembled from a plurality of individual parts.
The most different fluids are conceivable for operating the fluid pressure bearings. For example, water or oil can be used as a fluid. However, gases and especially air are especially advantageously used.
In a first embodiment, the connection between at least one of the bearing housings of the fluid pressure bearings and the bearing base body is generated in that at least one part of the rigid bearing base body and the bearing housing of at least one of the air bearings are manufactured monolithically from one block. In this way, the advantage results that an especially stiff assembly can be obtained between the bearing base body and the membrane. This is so because the bearing housings and especially the membrane as well as the bearing base body consist of a single part. Especially with respect to manufacture, the special advantage results that manufacturing is especially efficient because the separate manufacture of the bearing housing and of at least one part of the bearing base body (on which the bearing housing is included) can all be omitted.
In another embodiment of the invention, the bearing housing, which is configured as one piece, can also be a separate component which, in addition to the membrane, has a membrane holder and the bearing base body is directly journalled on the membrane holder for the connection between the bearing housing and the bearing base body.
In its simplest version, this second embodiment could be seen as an alternative to the bearing housing manufactured monolithically with the bearing base body. To clearly fix the bearing housing, a cutout could be provided in the bearing base body which exhibits a base or at least a projection on which the membrane holder of the bearing base body is mounted. Alternatively, it is also conceivable to journal the membrane holder directly on a planar surface of the bearing base body and to fix the latter, for example, via screws and pins against lateral slippage.
In an especially advantageous manner, the second alternative can be improved when the membrane holder is configured so as to be round and either the end of the membrane holder is configured so as to be a segment of a sphere and the base or the projection is configured as a truncated cone or the base or the projection is configured as a segment of a sphere and the end of the membrane holder is configured as a truncated cone. This embodiment affords the special advantage that, on the one hand, the bearing housing, which is configured as one part, is directly connected to the bearing base body and, on the other hand, the bearing housing is journalled so as to be rotationally movable on the bearing base body and thereby is self adjustable.
The two different embodiments, namely, the monolithic manufacture of the bearing housing in common with at least one part of the bearing base body and, on the other hand, the journalling of the membrane holder of the bearing housing, which is configured as one piece, on the bearing base body is then especially well combined when the bearing arrangement can be journalled simultaneously on at least two parallel guide surfaces but inclined toward each other. For this case, that particular fluid pressure bearing can be journalled on the first one of the two guide surfaces whose bearing housing is configured as one block in common with at least one part of the bearing base body. On the other one of the two guide surfaces, which are inclined toward each other, the second embodiment of the air bearing should be used whose bearing housing has the membrane holder. The bearing base body is journalled on the membrane holder of the bearing housing because this bearing can be configured to be self adjusting on the second guide surface as described above. This combination simplifies the production of the bearing base body considerably because the angle, which is conjointly defined by the two mutually inclined guide surfaces, can be maintained with high precision by the bearing base body when the fluid pressure bearings of the second guide surface would likewise be configured monolithically from a part of the bearing base body. Angles of this precision can be obtained only with considerable manufacturing complexity. For this reason, it is therefore purposeful to configure the bearings of the second guide surface to be self adjusting bearings in the manner described above even when this is associated with a modest reduction of stiffness.
The above two embodiments of bearing arrangements of the invention are especially advantageous when the fluid is supplied directly to the fluid-feed openings of the membranes and, in addition, a throttle is attached to the membrane. The throttle is fed via a fluid supply. In this way, the flow relationships can be individually changed for each individual fluid pressure bearing which is of special significance when several bearing housings are made together monolithically from a block with a part of the bearing base body. In this way, the total bearing arrangement can be correspondingly adjusted to the load conditions via a suitable selection of throttles. In order to have a possibility to correspondingly match the fluid pressure bearings especially even after the manufacture of the bearing base body, the throttle can be attached to the bearing housing so that it can be exchanged. One possibility would, for example, be that the throttle is threadably engaged in a winding provided in the membrane. Another possibility is, for example, to insert the throttle and to fixedly clamp the same via a corresponding catch.
It is especially advantageous when the bearing base body has at least one breakthrough for one of the fluid pressure bearings so that the bearing housing is accessible from the side of the bearing base body facing away from the bearing housing. In this way, the especially significant advantage is afforded that an exchange of the throttles is possible even after the assembly of the bearing arrangement on the guide and that the bearings can be correspondingly matched even at this point in time.